Reproductive hormones influence reproductive behaviors and nonreproductive behaviors by acting directly in the central nervous system. The proposed experiments have as a long-term objective an increase in our understanding of the neurochemical processes by which hormones affect behavior. Our model system for this purpose is the influence of estrogens on mating behavior in the rat, because sexual receptivity in the female rat is completely contingent upon recent exposure of the brain to estrogen. The proposed studies will examine the importance of temporal parameters of stimulation by estrogen to test the hypothesis that there are two phases to estrogen action during which different neurochemical processes are stimulated. Other studies will characterize the regulation of the synthesis and degradation of receptor proteins for estrogen, since these proteins initiate the response to the hormone within neurons. Finally, studies on these problems will be conducted on tissue slices in vitro in order to determine what the specific neurochemical products of estrogen action are. Studies of hormone action in the brain are related not only to fundamental emotional and behavioral systems, but also to the control of the entire reproductive system, all areas relevant to health and disease.